2l8 C. M. CHILD. 



This apparent double reversal in the susceptibility gradient 

 and the decrease followed by increase in susceptibility to KCN 

 requires some consideration. This case illustrates the difficulties 

 which immediately arise when susceptibility to one inhibiting 

 agent or condition is used as the measure of the action of another. 

 Until we know more concerning the changes preceding death in 

 such a case as this, it is impossible to reach any definite con- 

 clusion concerning the meaning of the changes in susceptibility, 

 but certain probabilities suggest themselves. 



In the first place the decrease in susceptibility and the more 

 or less complete reversal of the original gradient, the same 

 changes which have been observed in various species and under 

 various depressing or injurious conditions (Child, 'i6e, '17), 

 undoubtedly indicate a differential depression or injury along 

 the axis, the most susceptible, apical regions being so much more 

 injured than less susceptible, more basal regions, that the original 

 relations are often reversed. The point of interest is that 

 changes of this sort brought about by high temperature, con- 

 finement, etc., appear in the altered susceptibility gradient to 

 KCN. This apparently means that the action of these other 

 conditions and that of KCN on the protoplasm are not exactly 

 of the same sort, i. e., not strictly additive, for if they were, we 

 should expect the KCN simply to continue the action of the 

 high temperature or confinement without making them visible 

 as a reversed gradient and a decreased susceptibility. 



As death approaches, however, at least in the confinement 

 experiments, further changes apparently occur which differ from 

 those of the -earlier stages and these changes appear in increased 

 susceptibility to KCN and a second reversal of the susceptibility 

 gradient, a return to the normal basipetal condition. Under 

 ordinary conditions such increase in susceptibility would be 

 interpreted as associated with an increase in metabolic rate, 

 greatest in the apical regions, but it is impossible to believe that 

 in the later stages of confinement the cells approaching death 

 undergo any such increase in metabolic activity as these changes 

 w r ould indicate. It must be rather that in the later stages of 

 the decrease in metabolism which precedes death under these 

 conditions changes occur which are essentially like those pro- 



